Industrial applications of radiation polymerizable coatings, inks and films have significantly increased over the last several years. One factor that has lead to the great interest in radiation polymerization has been environmental concern and particularly efforts to reduce solvent pollution of the atmosphere. Furthermore, radiation polymerization as compared to more traditional methods of polymerization require much less energy along with the possibility of significantly reduced cure times.
The two major sources of energy for radiation polymerization currently employed are ultraviolet light and electron beam. However, of the two sources, electron beam is significantly more expensive in view of the high cost of equipment necessary for such processing. Accordingly, the commercial energy source most favored for radiation polymerization is ultraviolet light, which provides for photopolymerization.
Typically, the photopolymerizable compositions contain a photosensitive monomeric and/or polymeric material along with a photoinitiator, a photosensitizer and adjuvant materials for providing particular properties. Continuing efforts are underway to develop materials that exhibit particular characteristics desired for a particular industrial application and/or to reduce the expense of the compositions employed and/or of the process.
It is therefore an object of the present invention to provide a photopolymerizable process which does not require a photoinitiator.
It has been suggested in the past to polymerize certain unsaturated monomers using ultraviolet light, without the addition of any photosensitizing substance. However, the wavelength of the ultraviolet light required is typically so short as to require the use of light sources and reaction vessels constructed of fused quartz or another substance transparent to short ultraviolet light. For example, see U.S. Pat. No. 2,880,152 to Hiltz et al. Therefore, such a process is not practiced from a commercial viewpoint. Another problem with such previously suggested systems is that in many cases only a thin layer of material at the surface is polymerized.